Re: [RFC PATCH v7 07/25] vhost: Add reference counting to vhost_iova_tree

[Jason Wang]

在 2022/4/14 00:31, Eugenio Pérez 写道:
Now that different vqs can have different ASIDs its easier to track them
using reference counters.

QEMU's glib version still does not have them so we've copied g_rc_box,
so the implementation can be converted to glib's one when the minimum
version is raised.

Signed-off-by: Eugenio Pérez <epere...@redhat.com>
---


I'm not sure if it's too early to introduce things like this since we 
have at most 2 ASIDs. This is probably only needed when we want to 
expose ASIDs to guest.

Let's see how it goes for the following patch anyhow.

Thanks


  hw/virtio/vhost-iova-tree.h |  5 +++--
  hw/virtio/vhost-iova-tree.c | 21 +++++++++++++++++++--
  2 files changed, 22 insertions(+), 4 deletions(-)

diff --git a/hw/virtio/vhost-iova-tree.h b/hw/virtio/vhost-iova-tree.h
index 6a4f24e0f9..2fc825d7b1 100644
--- a/hw/virtio/vhost-iova-tree.h
+++ b/hw/virtio/vhost-iova-tree.h
@@ -16,8 +16,9 @@
  typedef struct VhostIOVATree VhostIOVATree;
  
  VhostIOVATree *vhost_iova_tree_new(uint64_t iova_first, uint64_t iova_last);
-void vhost_iova_tree_delete(VhostIOVATree *iova_tree);
-G_DEFINE_AUTOPTR_CLEANUP_FUNC(VhostIOVATree, vhost_iova_tree_delete);
+VhostIOVATree *vhost_iova_tree_acquire(VhostIOVATree *iova_tree);
+void vhost_iova_tree_release(VhostIOVATree *iova_tree);
+G_DEFINE_AUTOPTR_CLEANUP_FUNC(VhostIOVATree, vhost_iova_tree_release);
  
  const DMAMap *vhost_iova_tree_find_iova(const VhostIOVATree *iova_tree,
                                          const DMAMap *map);
diff --git a/hw/virtio/vhost-iova-tree.c b/hw/virtio/vhost-iova-tree.c
index 55fed1fefb..31445cbdfc 100644
--- a/hw/virtio/vhost-iova-tree.c
+++ b/hw/virtio/vhost-iova-tree.c
@@ -28,6 +28,9 @@ struct VhostIOVATree {
  
      /* IOVA address to qemu memory maps. */
      IOVATree *iova_taddr_map;
+
+    /* Reference count */
+    size_t refcnt;
  };
  
  /**
@@ -44,14 +47,28 @@ VhostIOVATree *vhost_iova_tree_new(hwaddr iova_first, 
hwaddr iova_last)
      tree->iova_last = iova_last;
  
      tree->iova_taddr_map = iova_tree_new();
+    tree->refcnt = 1;
      return tree;
  }
  
  /**
- * Delete an iova tree
+ * Increases the reference count of the iova tree
+ */
+VhostIOVATree *vhost_iova_tree_acquire(VhostIOVATree *iova_tree)
+{
+    ++iova_tree->refcnt;
+    return iova_tree;
+}
+
+/**
+ * Decrease reference counter of iova tree, freeing if it reaches 0
   */
-void vhost_iova_tree_delete(VhostIOVATree *iova_tree)
+void vhost_iova_tree_release(VhostIOVATree *iova_tree)
  {
+    if (--iova_tree->refcnt) {
+        return;
+    }
+
      iova_tree_destroy(iova_tree->iova_taddr_map);
      g_free(iova_tree);
  }